1. Field of the Invention
This invention relates to downhole sealing, and to an apparatus and method for use in forming an arrangement to allow creation of a downhole seal. Generally, the invention relates to the provision of a seal or packer between concentric downhole tubing, such as a bore-lining casing and production casing.
2. Background of the Related Art
In the oil and gas exploration and production industry, bores are drilled to access hydrocarbon-bearing rock formations. The drilled bores are lined with steel tubing, known as casing or liner, which is cemented in the bore. Oil and gas are carried from the hydrocarbon-bearing or production formation to the surface through smaller diameter production tubing which is run into the fully cased bore. Typical production tubing incorporates a number of valves and other devices which are employed, for example, to allow the pressure integrity of the tubing to be tested as it is made up, and to control the flow of fluid through the tubing. Further, to prevent fluid from passing up the annulus between the inner wall of the casing and the outer wall of the production tubing, at least one seal, known as a packer, may be provided between the tubing and the casing. The tubing will normally be axially movable relative to the packer, to accommodate expansion of the tubing due to heating and the like. The packer may be run in separately of the tubing, or in some cases may be run in with the tubing. In any event, the packer is run into the bore in a retracted or non-energized position, and at an appropriate point is energized or “set” to fix the packer in position and to form a seal with the casing. A typical packer will include slips which grip the casing wall and an elastomeric sealing element which is radially deformable to provide a sealing contact with the casing wall and which energizes the slips. Accordingly, a conventional packer has a significant thickness, thus reducing the available bore area to accommodate the production tubing. Thus, to accommodate production tubing of a predetermined diameter, it is necessary to provide relatively large diameter casing, and thus a relatively large bore, with the associated increase in costs and drilling time. Further, the presence of an elastomeric element in conventional packers limits their usefulness in high temperature applications.
Therefore, there is a need to provide a means of sealing production tubing relative to casing which obviates the requirement to provide a conventional packer, by providing a relatively compact or “slimline” sealing arrangement.
Additionally, recent industry trends have demanded the need for expandable tubular systems, where tubulars are expanded in situ. There is a need, therefore, for a packer that utilizes this in situ expansion technology. Also, some applications for packers now require high tensile strength and/or pressure ratings across the seal. These pressure ratings are conceivably as much as 10,000 psi or higher. There is a further need, therefore, for a packer using expandable tubulars that results in an exceptionally high sealing strength.